1. Field of the Invention
The present invention relates to an industrially advantageous process for producing 1,3,5-trichlorobenzene. More particularly, it relates to a process for producing 1,3,5-trichlorobenzene by chlorinating bromine-containing trihalobenzene (substitution of bromine atom with chlorine atom) in a vapor phase.
2. Description of the Prior Arts
1,3,5-Trichlorobenzene is important for industrial organic syntheses and it has been recently considered to be important as the starting material for explosives and various fine chemicals. It has been required to find an industrial process for production thereof.
Heretofore, 1,3,5-trichlorobenzene has been produced by various processes. For example, it has been proposed to produce 1,3,5-trichlorobenzene by isomerizing 1,2,4-trichlorobenzene in the presence of aluminum chloride and water at a refluxing temperature of 205.degree. to 212.degree. C. for 16 to 24 hours in U.S. Pat. No. 2,866,829. In this process, the condition of the reaction as the liquid phase reaction has been too severe and only about twenty and several % of 1,3,5-trichlorobenzene as the object compound has been obtained even though the reaction is continued for such long time. Moreover, the separation of the object compound from the reaction mixture has not been easy to be disadvantageous as the industrial process.
It has been proposed to produce 1,3,5-trichlorobenzene by chlorinating 1-bromo-3,5-dichlorobenzene in the presence of a catalyst of an azobisnitrile type compound or a benzoyl type compound in the liquid phase at about 65.degree. to 100.degree. C. in Japanese Unexamined Patent Publication 112827/1979. However, it has taken about 3 hours to complete this reaction. Moreover, a large excess of chlorine such as about 3 times of stoichiometrical amount of chlorine has been required and the catalysts are explosive to be dangerous. In the recovery of expensive bromine, it has required the complicated operations. Furthermore, the product has been contaminated by the catalyst or its decomposed material. These disadvantages have been found. In this process, bromine component is produced in a form of BrCl gas. In order to recover it as Br.sub.2, it has been required to produce Br.sub.2 by reacting chlorine gas with NaBr which is produced by reacting BrCl with an aqueous solution of NaOH. Moreover, Br.sub.2 is contaminated with a small amount of the catalyst or its decomposed product to cause the adverse effect to the following isomerization for producing 1-bromo-3,5-dichlorobenzene as the starting material.